1. Technical Field
This invention pertains generally to crystal regulated oscillators, and more specifically to crystal oscillator packaging.
2. Background
An oscillator circuit provides a stable-frequency output signal (typically sinusoidal) and, as those skilled in the electronics art will recognize, is an essential component for a variety of electronic devices that include communications equipment, navigation systems and data processing equipment. Many oscillators employ a piezoelectric quartz crystal as a mechanism for generating and maintaining a stable output signal. Quartz crystal ingots are grown and then sawn at different angles to produce crystals having different operating characteristics.
Quartz crystal resonant frequencies are temperature dependent. Stated alternatively, the output frequency of quartz crystals experience frequency shifts that are caused by temperature changes in the quartz element. When used in an oscillator circuit, the quartz crystal can cause the oscillator output frequency to shift as the quartz crystal""s temperature changes. The output signal of a quartz crystal oscillator can be kept steady over temperature by using circuits that sense temperature and which generate an appropriate corrective signal, which keeps the oscillator output frequency stable. Such a circuit is known as a temperature compensated crystal oscillator or xe2x80x9cTCXO.xe2x80x9d A TCXO is a quartz oscillator that employs active circuitry to generate a compensation signal that is used to keep the output of the oscillator device stable over wide-ranging temperatures. A TCXO can provide a very stable output signal over wide temperature swings and is a preferred oscillator in many communications applications and is the oscillator of choice where highly stable frequency sources are required. As with all electronic components, however, TCXOs have become increasingly smaller. It is now known to package the quartz crystal in the same package as the compensation and oscillator circuitry, which is typically embodied as an integrated circuit. The footprint of a TCXO can be significantly reduced if the TCXO is fabricated in a multi-layer housing wherein an IC is mounted and electronically coupled to the quartz crystal resonator.
A prior art methodology for reducing the footprint of a TCXO includes using a multi-layer housing that contains a quartz crystal resonator on one layer, and mounts the active electronic oscillator/compensation circuitry on another layer. Directly mounting an IC on a ceramic layer has been proven to be somewhat problematic when the package is constructed with cavities on both the top and bottom of the package. The relative non-planarity of a ceramic IC carrier layer can be so significant such that an integrated circuit, which is highly planar and which needs to be mechanically bonded to the ceramic carrier layer, can be damaged during the course of bonding an IC to the ceramic carrier layer.
An improved TCXO that avoids the manufacturability problems associated with multi-layered, multi-cavity ceramic housings, and in particular the tendency of integrated circuit devices to fracture or otherwise fail upon mounting to a ceramic carrier layer, would be an improvement over the prior art.
There is provided a TCXO that includes a multi-layer housing in which an integrated circuit (providing active circuitry for oscillation and to compensate for temperature variations in a quartz resonator) is mounted on a layer having an evacuated region which allows contact pads on the IC to mechanically couple to and mate with corresponding pads on the carrier surface such that the IC substrate does not directly contact the carrier surface.